Paper hearts

Y/N is eleven when she wakes up in a back alley with no idea how she got there.

The doctors think she has amnesia.

She lets them.

After all, "I woke up in another world" sounds considerably less believable.

Unfortunately for her, the new world she's stumbled into just so happens to be one she vaguely remembers from somewhere.

Or:

An isekai JJK fic where Y/N is far less overpowered than she'd like, accidentally invents one of the most annoying cursed techniques imaginable, collects emotional trauma like Pokémon cards, and somehow ends up with half of Jujutsu High refusing to let her out of their sight.